1. Field of the Invention
The present invention relates to a driving device for quickly changing the gray level of the liquid crystal display and its driving method, especially to a display driving device and its driving method, which can simultaneously or synchronously drive a plurality of thin film transistors, wherein the source and the gate of each thin film transistor in the driving device are respectively connected with different gate lines and data lines to let the specific transistor be driven by the gate driver and the source driver, and the voltage of displaying the present frame interval data or the voltage of displaying black image is applied to accomplish the object of quickly changing the gray level of the liquid crystal display. The present invention can suit for the picture treatment of various liquid crystal displays, organic light emitting diode (OLED) display or plasma display panel (PDP).
2. Description of the Prior Art
Because the liquid crystal display possesses the advantages of low power consumption, light of mass, thin thickness, without radiation and flickering, it gradually replaces the traditional cathode ray tube (CRT) display in the display market. The liquid crystal display is chiefly used as the screen of the digital television, the computer or the notebook computer. In particular, the large sized liquid crystal display is widely used in the amusements of the life, especially in the field in which the view angle, the response speed, the color number, and the image of high quality are in great request. But there exist some limitations and drawbacks due to the properties of the liquid crystal molecules such as viscousity, elasticity, and dielectricity etc.
Referring to FIGS. 1A and 1B, they are the simple schematic views showing the internal structure of the prior liquid crystal display. Mark 10 is the display panel. The data driver 11 is installed above the display panel, which can change the data of the adjusted gray level signal into the corresponding data voltage. The image signal can be transferred to the display panel 10 through the plurality of data lines 111 connected with the source driver 11. The gate driver 12 is installed on one side of the display panel 10, which can continuously provide scanning signal. The scanning signal can be transferred to the display panel 10 through the plurality of gate lines 121 connected with the gate driver 12. The data line 111 and the gate line 121 are orthogonally crossed and insulated with each other. The area enclosed in them is a pixel 13.
After the image signal is output from the data driver 11, it will get to the source of the thin film transistor Q1 in the pixel 13 through the data line D1, and a control signal is correspondingly output from the gate driver 12, it will get to the gate of the thin film transistor Q1 through the gate line G1. The circuit in the pixel 13 will output the output voltage to drive the liquid crystal molecular corresponding to the pixel 13, and a parallel plate type capacitor CLC (capacitor of liquid crystal) will be formed by the liquid crystal molecules between the two pieces of glass substrates in the display panel 10. Because the capacitor CLC cannot keep the voltage to the next time of renewing the frame data, so there is a storage capacitor CS provided for the voltage of the capacitor being able to be kept to the next time of renewing the frame data. This display mode is called “Hold type”.
Although the brightness between the frame and the next frame in the liquid crystal display can be kept and the flickering phenomenon of the frame in the traditional CRT display cannot be produced, there still exists another problem of afterimage phenomenon. It can be explained with FIG. 2. If the brightness of the four frames F1, F2, F3, and F4 in the time axis are be displayed on the liquid crystal display, the pixels of the panel need be driven by the source drivers and the gate drivers of the liquid crystal display to change the brightness of the panel. Because there exists a response time for the rotation of the driven liquid crystal molecules, the brightness will change with the time as shown by curve (a) in FIG. 2. After the expected brightness is reached, the brightness is maintained by the voltage of displaying the frame. If the response speed of the liquid crystal molecular is not quick enough, the image of the preceding frame and the image of the following frame will overlap each other to blur the image, i.e. the afterimage phenomenon. Especially when the ascending speed is quicker than the descending speed in the brightness variation of the liquid crystal display, the afterimage phenomenon during the frame change can be easily produced.
The color of the traditional. CRT display is produced by the strike of the electron beam on the screen coated with phosphorescent material. The color produced by excitement occurs instantaneously and disappears quickly. The excitement for the image of the following frame is continued. This is the so-called impulse type display. The brightness variation of its display is shown as curve (b) in FIG. 2. Therefore, no afterimage occurs between the frame and the following frame. But if the scanning frequency of the CRT display is not quick enough, the flickering phenomenon will be produced.
The resolve the drawback of the afterimage phenomenon of LCD and possess the advantage of the impulse type CRT, at present there is a pseudo impulse type technique for the display of the image data. Referring to FIG. 3, the said object can be accomplished by two techniques in theory stated as below:    (1) The black color data or the black image is inserted in the continuous image frame: if F1, F2, F3, and F4 are the frames of the series of continuous image, the black images B1, B2, and B3 can be inserted between the continuous image frames with a multiple scanning frequency. After the expected brightness of the display is reached, it can be removed by the black image data. This method can simulate the display of CRT.    (2) The black image signal is inserted in the back light source to make the back light source flicker: The brightness of every frame is originally provided by the light source at the back of the display panel. If L1, L2, L3, and L4 are the continuous back light source and the black image signals are inserted between the back light sources, the light source can be forced to close and produce the black image B1, B2, and B3. This method can also get the effect of simulating the display of CRT and remove the afterimage phenomenon.
Therefore, the present invention discloses a driving device for quickly changing the gray level of the liquid crystal display and its driving method to simulate the pulse type display of CRT and remove the afterimage phenomenon of the liquid crystal display.
In view of this, the inventor had the motive to try and develop the present invention after hard study.